In order to grow beyond minimal size, tumors must induce a new blood supply. Like many human carcinomas, renal cell carcinomas (RCC) are thought to induce angiogenesis by secreting an angiogenic cytokine, vascular permeability factor, also known as vascular endothelial growth factor (VPF/VEGF). Studies from several laboratories, including our own, have shown that a number suppressor gene, the von Hippel Lindau (VHL) gene, has an important role in regulating VPF/VEGF expression in RCC and that this regulation involves both transcriptional and post-transcriptional events. More recently, they have found that wild-type VHL (wt-VHL) selectively interactions with and thereby down-regulates the activities of two protein kinase C (PKC) isoforms, rho and sigma; when VHL is as functional, as in RCC, VPF/VEGF is overexpressed, suggesting that PKC rho and sigma are on the signaling pathway(s) by which VHL regulates VPF/VEGF expression. Other evidence suggests that oncogenes, notable Ras and Src, also regulate VPF/VEGF expression in several important tumors, likely also including RCC. The experiments proposed here are designed to investigate more carefully the signaling pathways by which a tumor suppressor gene (VHL) and oncogenes (Ras, Src) induce VPF/VEGF overexpression and thus angiogenesis in RCC. A first Aim will make use of dominant negative mutants of PKC rho and sigma in RCC cells to investigate the role of PKC rho and sigma in regulating VPF/VEGF expression at both transcriptional and post-transcriptional levels. The nature and consequences of physical interaction between PKC and wt-VHL will also be explored. For Aim 2, dominant negative mutants of Ras and Src will be utilized to investigate whether and by what pathways these signaling components regulate VPF/VEGF expression in RCC. Finally, a third Aim will determine whether RCC cells transfected with dominant negative mutants of PKC rho and sigma or of other protein kinases along the signaling pathways which regulate VPF/VEGF expression, down-regulate VPF/VEGF and inhibit tumor angiogenesis and growth in an animal model. These experiments will provide new and important information on the mechanisms of carcinogenesis and suggest new targets for intervention in RCC, a common, highly vascular, angiogenesis-dependent carcinoma that is resistant to currently available therapeis.